"I'm frustrated and I'm angry at this point," said Robert Spierer, Lauren's father, on Katie Couric's syndicated talk show. "We've been stonewalled to some extent by the last people to see Lauren. Despite their claims of doing whatever they could do, the fact of the matter is that they refused to meet with us except for one of the boys. They refused to take a police polygraph, which we feel is important for a number of reasons, one of which is to help narrow down the field of people who really know what happened to her that night."

Renowned TV host and crime-victims advocate John Walsh, appearing with Spierer's parents on the ABC show, urged anyone with information about her disappearance to "have the courage" to come forward and ease her parents' suffering.

Walsh, who gained fame as host of America's Most Wanted, said he knew first hand the increasing pain and frustration the family has endured since the 20-year-old college sophomore disappeared early June 3, 2011.

Walsh's own 6-year-old son, Adam, was kidnapped and later found murdered in 1981, a crime that took nearly three decades for police to solve.

"My heart goes out to this family," Walsh said of the Spierers. "This is somebody's beautiful daughter.If you have any information, why not be forthcoming? The police are stonewalled. Somebody knows what happened to this girl.

"What they want is they want to know," he told Couric. "Somebody knows something, Katie, and somebody has to have the courage. They can remain anonymous, but just have the courage to end these people's pain."

Lauren Spierer was last seen at 4:30 a.m. walking toward her off-campus apartment in Bloomington, Ind., after a night of heavy drinking with friends. The 4-foot-11, 95-pound co-ed has not been seen since.

The family created a Facebook page and hired private detectives to search for clues, and have made numerous public pleas for anyone with information to come forward.

"I don't think we discovered the right information because we don't still have Lauren," Charlene Spierer said. Asked by Couric about her own theory about what happened to her daughter, she said, "I surely don't think it was a random abduction. I think that somebody that Lauren knew was responsible for the events of that evening."

In June, one year after she went missing, a (Westchester, N.Y.) Journal News investigation revealed that Spierer was so inebriated before her disappearance that she had to be carried up the street on the back of a friend.

The report, based on an extensive review of records and interviews with several people close to the case, found that Spierer had fallen so frequently that one of her eyes had begun to blacken, she had smacked her skull and lost her keys, her shoes, her cellphone and her ID.